Various scenarios exist where it is desirable to delay the initiation of an event until some time after an initial shock or acceleration. By way of example, in order to prevent premature detonation, many munition rounds, such as artillery shells, go through a multi-stage arming sequence after being fired. It is required that the sequence commence only after the shell has been fired, and for this purpose a delay after firing is imposed in the procedure.
One way of providing the necessary delay is by the use of an accelerometer. One problem with the accelerometer, however, is that it requires not only a power supply but a signal processor as well. Such arrangement needs a significant volume to package the necessary components, which is impractical for various situations, including use in a munition round.
The delay may also be accomplished by an inertial delay mechanism, one of which is known as a falling leaf delay mechanism comprised of a plurality of interlocking masses wherein a subsequent mass is prevented from moving until the previous mass has moved out of the way. The typical falling leaf delay mechanism is comprised of a first series of masses rotatable about a first post and a second series of masses, interlocked with the first series, rotatable about a second post. Each mass, except for the first, occupies a plane above a previous mass. When the mechanism is subjected to a shock, a first mass of the first series is moved out of position allowing a first mass of the second series of masses to move out of position. That is, movement of a mass allows the next interconnected mass to move out of position. A last of the masses to move includes an activation member to activate some event, the activation occurring after a time delay imposed by movement of the totality of all the masses, subsequent to the initial shock.
Existing falling leaf designs require masses, which are individually machined, followed by an assembly process. The required assembly is either by hand, a time consuming process, or by expensive machine placement. In addition, present designs are relatively large for placement in munition rounds and do not respond to relatively low acceleration environments.
It is an object of the present invention to provide an inexpensive miniature inertial delay device which can respond to low accelerations and which is fabricated utilizing MEMS (micro electromechanical systems) techniques.